Core binder



United States Patent CORE :BINDER Jacob W. Sietsema, Northbrook, 11]., assign'or to International Minerals & Chemical Corporation, a corporationof New York No Drawing. Filed Dec. "30, 1957, .Ser. No. 705,793

4 Claims. (Cl.' 106'38.'5)

The present invention relates to cores for foundry purposes. More particularly, it relates to a foundry core of high baked strength, imparted by a novel binder component.

In the casting of metals, void :spaces in the casting are produced by incorporating cores of one sort or another in the mold. Such cores, like the mold itself, are made of sand, and must include some kind of binding material to withstand the eroding action of the molten metal. Inasmuch as the cores are largely surrounded by the molten metal, the requirementsfor a satisfactory binder are a great deal more severe than for the external mold itself. A great deal of work has accordingly been done in the field of core binders. Numerous materials have been used for this purpose in the past, including cereal products, water glass, drying oils, resins, sulfite liquor, proteinaceous materials, molasses,-olays, woodfiour, gelatinized starches, dextrinized starches, and many -other substances. In each case, it is usually found necessary to ad done or more additional binder componentsin order to produce a core approaching the desired properties. Most of the prior-art binders are capable of producing adequate green strengt i.e., sufficient strength to permit the core to be 'transferred'into a baking zone. The various prior-art materials vary greatly, however, in their so-called baked strength (he, their strength after being baked, which must be suflieient -to withstand the impact and the stresses produced by themolten metal) and in their hot properties (these being the ability of the core to withstand the molten metal until solidification is Well advanced, and then .togive way thereafter so as to avoid imparting stresses in the casting). The present invention relatestoan improved core binder component which has the property of imparting remarkably.high'bakedstrength in foundry cores, without interfering in any way with the hot "properties thereof.

An object of the present invention is to produce an improved foundry core. I

Another object is tolprovide an improved core binder component.

Another object is to provide a core binder component capable of imparting high baked "strength without interfering with the hot properties *of'the core.

Another object is to segregate the fraction of gelatinized starch capable of imparting high baked strength to foundry cores, and to remove deleterious substances therefrom.

Other objects of the invention will be apparent from the present description and claims.

I have now found that gelatinized amylopectin is extraordinarily effective as a component of corebinders to increase the baked strength of the resulting cores. For this purpose, gelatinized amylopectin is employed in a form substantially free from amylose and preferably substantially free from fats, proteins, fibers, and other substances commonly found in associationtherewith, and is incorporated in a foundry core in a proportion between ice 2 portion of water between about '2 andabout"6% liy weight, based on the weight of the dry mixture. The

amylopectin is preferably employed in the form .ofa

powder, whichis mulled or otherwise blended 'into a core sand in the desiredproportion, optimally between about 0.5 and about 1.5% by weight. The water is preferably blended into the sand before the amylopectin. Amy-lopectin can also be added to other core-binder compositions, e.g., gelatinized starch, cereal (corn flour), or the like, to improve the baked strength thereof. Tne completed core mixture, when properlyblended, formed into the desired shapes, and baked, yields cores having a baked tensile strength as-high as 250 psi. or more.

Starch appears .to be composed of two types of molestiles-a straight-chain fraction called amylose, and a branched-chain fraction called amylopectin. These two fractions are known .to .differsubstantially in physical and chemical properties, such as solubility, enzy-rne digestibility, color formation with iodine, crystallinity, viscosity in aqueous dispersion, and in other respects. The separationof the .two "fractions in their original form does not appear to have'been accomplished. In every case, it has apparently been necessary to subject the starch grantiles to at least a swelling treatment with water as a preliminary to separating the fractions. It has been reported that amylose can be extracted with hot water. from swollen corn starch granules. The most eifective-separation technique, however, starts with a starch"paste,; i.e., a dispersion prepared by boiling starch with water. From such a dispersion, amylose can be selectively precipitated by addition of butanol orpentanol, leaving the amylopectin in solution '(Schoch, Cereal Chem, 18 (1941)., 121; J. Am. Chem. Soc., 64 (1942), 2957).

The amylopectin thus obtained is, of course, a ,gelatinized form of the original amylopectin. This is the material which I have found to be particularly effective in .producing foundry cores of high baked strength without impairing the hot properties thereof. The dispersion can be used directly as an additive to a core mixture, preferably after distilling off the butanol or pentanol, and preferably after evaporating to produce an appropriate ratio of amylopectin and water as desired in the final core mixture. More conveniently, however, the amylopectin dispersion can be evaporated to dryness, suitably in a spray dryeror by use of a concentrator and a drum flaker, yielding a .solid product which is readily stored, handled, and admixed with foundry sands. When the solid ma terial is added to sand, the mixture should be blended, commingled with water in the desired proportion rererably around 3 to 5% by weight) and again blended before being shaped andbaked.

I have discovered that the effectiveness of gela'tinized amylopec'tinis far in excess of what might be expected about 0.1 and about 3% 'by weight, together with a profrom'theprioraart use of gelatinized. starch in cores. "It appears that the other constituents in gelatinized starclr' a'ct'not merely'as diluents but as active adulterants, greatly reducing the effectiveness of the amylopectin. When such materials are removed (particularly the amylose), the purified gelatinized amylopectin produces a baked strength more thantwice as great as might be expected from its behavior in the form of crude gelatinize'dstarch.

Another remarkable property of gelatinized amylopectin lies in its ability to produce a baked core, at ordinary temperature; 'i.e., when a core containing the purified material is merely allowed to stand at room temperature, it undergoes chemical and physical changes of unascertained nature which result in high baked strength Without actual baking in the manner practiced by the prior art. It is, of course, feasible to carry out a conventional type of bakingto hasten the processj but even when this is done, the temperatures and the baking 7 2,914,048 Patented Mar. 7, 196i -prior art to accomplish essentially the same result. The baking can satisfactorily be carried out, for example, at temperatures as low as around 300 to 400 F. for periods of as little as to 15 minutes.

In an especially advantageous modification of my invention, gelatinzed amylopectinis employed as a core binder in combination with an alkali-metal phosphatemodified starch, prepared as described by Neukom in US. Patents 2,884,412 (April 28, 1959) and 2,865,762 (December 23, 1958). In the Neukom method, dry, ungelatinized starch is impregnated with an aqueous solution of an alkali-metal orthophosphate salt having a pH between about 4 and about 7, optimally around 6, then dried to less than about 15% water content, and heated at a temperature between about 125 and about 200 0., preferably between about 150 and about 175 C., for a period of about 1 to about 15 hours, the heating time varying inversely with the temperature. A modified starch is obtained thereby, having the property of dispersing rapidly in cold water to produce dispersions having a viscosity between about 1,000 and about 5,000 cp., measured in 5% aqueous dispersion at room temperature. Such modified starches are highly useful in core binders, producing cores of good hot properties. The baked strength of such cores (and of foundry cores in general) is materially improved by including gelatinized amylopectin in the binder, suitably in a proportion between about and about 75% by weight, based on the total binder.

As defined in Neukom US. Patent 2,884,412, the Neukom starch phosphates are substances prepared by impregnating an ungelatinized starch with at least about 1.0% by weight, calculated as phosphorus, of at least one phosphate salt of an alkali-metal in an aqueous solution of said salt having a pH between 3.0 and about 7.5, and heating the impregnated starch in the substantial absence of unabsorbed water at a temperature between about 120 and about 175 C. for a period of about 1 to about hours.

For the preparation of phosphate-modified starches, the preferred phosphate salts are the sodium, potassium, and lithium orthophosphates, alone or in suitable combinations with themselves and/or with orthophosphoric acid to yield a pH of the desired level in aqueous solution. The impregnating solution may suitably be between about 1 and about 3 molar in phosphate, and should be used in a quantity equivalent to at least about 1% by weight of phosphorus, preferably between about 3 and about 5%, based on the quantity of starch to be treated. The starch and solution are slurried together in the desired proportion for 5 to 10 minutes or more, then separated. The starch is dried at a temperature below its gelatinization point, ordinarily below about 60-80 C., depending upon the particular starch, to a moisture content around 8 to 15% or somewhat lower, and is then subjected to heat treatment as described hereinabove. The baked material is a phosphate-modified starch suitable for use as a core binder, and advantageously useful in combination with gelatinized amylopectin in accordance with my invention.

The invention will be more clearly understood from the following operating examples. All of the tests described therein were carried out according to standard methods defined in the Foundry Sand Handbook, Sixth Edition (1952), published by the American Foundrymens Society, Chicago. All measurements are on a dry basis. In each case, the cores were prepared and tested in triplicate, and the reported results are the average of the three tests.

Example I .The following test illustrates the use of gelatinized amylopectin alone as a core binder. The resulting core had excellent baked strength, but relatively low hot strength.

No. 1 steel sand having an AFS grain fineness of 65 (AGF 65) was mulled with 5% by weight of water for 1 minute; then 1% of substantially pure, dry, gelatinized amylopectin was added, and mulling was continued for 6 minutes. The completed mixture retained 5.0% water. Standard test cores prepared therefrom had a green strength of 0.95 p.s.i. After they were baked 20 minutes at 425 F., their tensile strength at break was 265 p.s.i.

Standard cores were then prepared for measurement of the hot strength of the core mixture, measured in terms of the time required for a 1%" dia. x 2 cylindrical test core to collapse under a -lb. load at a given oven temperature. In each case, the test cores were The following illustrates a mixed core binder consisting of a conventional cereal-type binder plus gelatinized amylopectin.

No. 1 steel sand, AGF 65, was mulled with 5% water for 1 minute; then 1% of corn flour and 0.25% of dry, gelatinized, substantially pure amylopectin were added, and mulling was continued for 6 minutes. The completed mixture retained 5.0% of moisture. Standard test cores prepared therefrom had a green strength of 0.85 p.s.i. When baked at 425 F. their stength was as follows:

Baking Baked Time, Strength,

min. p.s.i.

Hot-strength test cores, baked 20 min. at 425 F., had

the following properties:

Oven Time for Temp., Collaps F. min.

Example 3 The following test illustrates the use of gelatinized amylopectin in combination with a technical-grade sodium phosphate-modified corn starch, prepared as described above, containing about 4.04% phosphorus and having a viscosity of 6310 cp. at 25 C. in 5% aqueous dispersion.

No. 1 steel sand, AGF 65, was mulled with 5% water for 1 minute; then 1% of a 50:50 mixture of the phosphate-modified starch and dry, gelatinized, substantially pure amylopectin was added, and mulling was continued for 6 minutes. The completed mixture contained 5.2% water. Standard test cores prepared therefrom had a green strength of 0.80 p.s.i. and a baked strength (20 min. at 425 F.) of 225 p.s.i. The baked cores had hot strengths as follows:

Oven Time for Temp, Collapse,

F. min.

Example 4 The core mixture of Example 3 was repeated, except that it was prepared with 3.2% of water, and the completed mixture contained 3.1% of water. Standard test cores had a green strength of 1.05 p.s.i., and developed high baked strength at temperatures as low as 300 F.:

Baked Strength, p.s.i. Baking Time, min.

300 F 400 I 450 F.

Even at room temperature, the green cores cured to a baked strength of 145 p.s.i. in 16 hours.

Example 5 The core mixture of Example 3 was repeated, except that the proportion of phosphate-modified starch to amylopectin was :60. The completed mixture contained 5.0% water. The test cores had a green strength of 1.25 p.s.i. and a baked strength (20 min. at 425 F.) 35

In accordance with the foregoing description, I claim as my invention:

1. in a method for the production of a foundry core from a mixture of sand, wat and hinder, the improvement which comprises employing as said binder a starch;

fraction consisting of gelatinized amylopectin in a proportion sufficient to produce a core of improved baked strength.

' 2. In a method for the production of a foundry core from a mixture of sand, Water, and binder, the improvement which comprises incorporating into said mixture a starch fraction consisting of gelatinized amylopectin in a proportion sufiicient to produce a core of improved baked strength.

3. The method of claim 2 wherein said binder includes a starch phosphate prepared by impregnating an ungelatinized starch with at least about 1.0 percent by Weight, calculated as phosphorus, of at least one phosphate salt of an alkali metal in an aqueous solution of said salt having a pH between 3.0 and about 7.5, and heating'the impregnated starch in the substantial absence of unabsorbed water at a temperature between about and about C. for a period of about 1 to about 15 hours, the length of the heating period varying inversely with the temperature.

4. In a method for the production of a foundry core from a mixture of sand, water, and cereal binder, the improvement which comprises incorporating into said mixture as an added binder a starch fraction consisting of gelatinized amylopectin, the quantity of said starch fraction being sufiicient to produce a total proportion of gelatinized amylopectin between about 10 and about 75% by weight, based on the total binder, whereby a core of improved baked strength is obtained.

References Cited in the file of this patent UNITED STATES PATENTS 1,938,574 Bauer Dec. 12, 1933 1,974,915 Giesecke Sept. 25, 1934 2,779,693 Pacsu et a1. Jan. 29, 1957 2,884,412 Neukorn Apr. 28, 1959 FOREIGN PATENTS 543,202 Great Britain Feb. 13, 1942 OTHER REFERENCES Foundry, February 1950, page 177. 

1. IN A METHOD FOR THE PRODUCTION OF A FOUNDRY CORE FROM A MIXTURE OF SAND, WATER, AND BINDER, THE IMPROVEMENT WHICH COMPRISES EMPLOYING AS SAID BINDER A STARCH FRACTION CONSISTING OF GELATINIZED AMYLOPECTIN IN A PROPORTION SUFFICIENT TO PRODUCE A CORE OF IMPROVED BAKED STRENGTH. 